1. Field of the Invention
This invention relates generally to friction welding, and particularly to friction welded parts having a flash trap. The invention provides friction welded parts with a novel sealed flash trap and a method of producing such parts.
Friction welding is a well-known manufacturing process which uses axial force and rotational motion to heat a circular interface (solid or tubular) by friction, plasticizing and upsetting material into "flash rolls" while losing axial length, and then arresting the rotational motion and usually increasing axial force, to form a solid state forge bond between two or more components. It may be performed either on continuous drive friction welding machines using a constant speed motor drive, or on inertia friction welding machines which store kinetic energy in a flywheel attached to the machine spindle and disperse that energy to the weld interface when axial force is applied, or on hybrid machines combining both methods.
Although conventional friction welding results in a totally random stopped position, specifically equipped machines with an "angular orientation" capability may be used to align asymmetrical features on opposite sides of the symmetrical interface by stopping the machine spindle in the same location every cycle.
Flash is of course inherent in friction welding. In some applications, the flash can be ignored, but in other applications cannnot be tolerated. The flash may have small particulate matter which could break away and cause problems, or an oxidized flash scale which may also break free to cause problems. In some applications, even minute particles breaking away from the flash cannot be tolerated. For example, in hydraulic cylinders, where the end of the cylinder may be friction welded to the body, contamination as small as 10 microns cannot be permitted.
2. Description of the Prior Art
In the past, this problem has meant that friction welding could not be used for certain applications, unless elaborate steps were taken to eliminate the flash, e.g. by machining, or by using some form of sealant to seal off the area of the weld from the area to be kept uncontaminated.
External and internal (for tubular welds) flash may be removed by shearing tools, turning tools, or boring tools on the welder. Alternatively, "flash traps" may be used to partially isolate internal or external flash rolls. A flash trap, in the case of an internal flash trap, is typically in the form of a solid cylinder of diameter slightly less than the inner diameter of the hollow cylindrical part, extending along the hollow cylindrical part back from the region of the weld, and having an annular recess in the region of the weld. The flash is "trapped" in this annular recess. However, there must normally be some clearance between the rotating components, i.e. between the hollow cylinder and the solid flash trap cylinder, so that the concentricity limitation (accuracy under load) of the machine used does not result in "rubbing" or "pickup" away from the friction surfaces, with consequent damage and creation of scale and loose particulate matter. The existence of this clearance provides a path for small particulate matter to escape the trap. In the prior art, that clearance in flash traps of this and other configurations has been sealed by subsequent operations using epoxy, "O" rings, conventional welding, etc., which renders the production of the parts somewhat uneconomical.